1. Field of the Invention
The present invention is directed to a vibration damping system for a motor vehicle drive system of a motor vehicle which includes an electric machine controllable by a control device for exerting a counter-torque on a rotating constructional group.
2. Description of the Related Art
A vibration damping system is disclosed in German reference DE 195 32 129 A1 in which movement irregularities of a shaft may be actively reduced by appropriately controlling an electric machine. The electric machine receives information from a control device including indications of the occurrence of movement irregularities. The information regarding the movement irregularities may be indicated in secondary quantities such, for example, as the rotational speed of the machine, the throttle position, or other parameters related to the rotational speed of the machine. The occurrence of movement irregularities is compulsorily expected in certain operating states. A control variable for the electric machine is taken from a characteristic field corresponding to the respective operating state and the electric machine is then operated to generate a counter-torque to the movement irregularities expected at the respective operating state. It is also possible to detect occurring movement irregularities directly and to minimize them correspondingly in a regulating process.
The electric machine used in this known system may simultaneously provide a supporting force for an internal combustion engine or act as a generator of electric energy so that electric energy is also generated during the vibration damping function to feed consumers present in the vehiclexe2x80x94i.e., lights, radioxe2x80x94or to charge a battery.
This system inherently includes a number of problems. During relatively strong vibrations having large amplitudes, there is the risk that the energy required by the electric machine for damping these strong vibrations is so great that a suitable supply of energy from the electric machine to electric consumers in a vehicle is no longer ensured during the vibration damping function. Further, a characteristic of electric machines is that the torque decreases as the speed increases. Accordingly, movement irregularities occurring chiefly at high speeds may not be suitably damped. To counter these two problems, the electric machines in known systems must be dimensioned so that they are large enough to guarantee a sufficient vibration damping function at high rotational speed and a sufficient supply of electric energy to the consumers during strong vibrations. Further, the overall efficiency of the drivetrain is reduced by the active vibration dampingxe2x80x94especially during the operating states of the drive system requiring counter-torque generationxe2x80x94thereby increasing the fuel consumption of the internal combustion engine.
The object of the present invention is to provide a vibration damping system for generating suitable vibration damping in a simple and economical construction essentially independent from the operating state while simultaneously achieving a high efficiency of torque transmission and a low energy consumption of the driving source.
According to the invention, this object is met by a vibration damping system for a drive system of a motor vehicle comprising an electric machine controllable by a control device for exerting a counter-torque on a rotating constructional group.
The inventive vibration damping system further comprises a deflection mass arrangement in a rotating constructional group of the drive system that is rotatable about an axis of rotation. The deflection mass arrangement has at least one deflection mass and a deflection path associated with the at least one deflection mass and along which the at least one deflection mass is movable. The deflection path associated with the at least one deflection mass has a vertex area which is an area with the greatest radial distance of the deflection path from the axis of rotation of the rotating constructional group and deflection areas proceeding from the vertex area.
The vibration damping system according to the invention includes two systems for countering occurring movement irregularities. The first system for countering movement irregularities is the electric machine which may provide a high counter-torque especially in the low speed range and accordingly ensures suitable vibration damping. The second system for countering movement irregularities is the deflection mass arrangement which may exercise its vibration damping action or vibration eliminating action especially when the deflection masses excited to oscillation are deflected from a sufficiently strong centrifugal potential. This latter situation ultimately requires a sufficiently high rotational speed of the rotating constructional group. The two systems supplement one another. Moreover, the energy to be applied by the electric machine for vibration damping may be reduced even at low rotational speeds by the counter-torque provided by the deflection mass arrangement. Accordingly, the deflection mass arrangement according to the invention provides a vibration damping or vibration eliminating function even at low rotational speedxe2x80x94i.e., with low centrifugal force. Due to the weaker centrifugal potential at lower rotational speeds, the risk that the deflection masses will reach the respective end areas of their deflection paths and will strike against the ends of their deflection paths is heightened. The striking would lead, in principle, to a detuning of these oscillators. However, the electric machine may be used to generate a counter-torque to an occurring vibrational excitation in the area of operation in which the striking of the deflection masses is anticipated. This may be achieved to an extent such that, while not entirely eliminating the induced vibrations already by the action of the electric machine, these vibrations are nevertheless weakened to the extent that the movement irregularities which still remain and which act on the deflection mass arrangement no longer cause the deflection masses to strike against their path ends. Therefore, the electric machine is operated only to the extent that is required to keep the deflection mass arrangement within its normal operating range, i.e., in an operating range in which the associated deflection masses cannot strike against their path ends at respective stop areas. In this way, the energy to be applied by the electric machine for damping vibrations may be minimized in the low-speed range which allows the use of smaller electric machines and allows the electric machine to provide sufficient electric energy for additional consumers, if required, in this operating range. The overall effect is that energy consumption is reduced.
The control device of the present invention, for example, may be arranged for receiving information about movement irregularities that are anticipated or that occur during rotation of the constructional group and controlling the electric machine so that the counter-torque exerted by the electric machine counters the anticipated or occurring movement irregularities. The information about movement irregularities may be derived directly from movement irregularities detected in the system as well as indirectly from the operating point of the internal combustion engine. The operating point of the internal combustion engine may, for example, be derived from the rotational speed, the throttle opening, and/or the intake pipe pressure of an internal combustion engine. It is well-known that movement irregularities occur in a compulsory manner in certain operating states that are defined by such quantities.
As mentioned above, the control device may be arranged for controlling the electric machine for generating a counter-torque for eliminating movement irregularities only in a range of low rotational speed such as less than 1800 revolutions/minute or, at most, less than 1000 revolutions/minute because the torque output of an electric machine decreases as the rotating speed increases.
However, beyond this, the control device may also control the electric machine for generating the counter-torque for predetermined frequencies, predetermined frequency ranges, and/or a predetermined type of movement irregularity independent from the rotational speed of the rotating constructional group. While it is taken into account that, in principle, the efficiency of the electric machine at higher speeds is reduced, the electric machine may be used at higher speeds in an attempt to counter vibrational excitations which would excessively impair the driving comfort or the driving behavior of a vehicle using all available means.
Further, the electric machine preferably generates a basic braking torque or driving torque for supplying the onboard power supply. The generation of the counter-torque is superimposed on the generation of the basic braking torque or driving torque when movement irregularities occur.
The deflection path of the at least one deflection mass has deflection areas that may extend in opposing axial directions proceeding from the vertex area and/or the deflection areas may extend in opposing circumferential directions proceeding from the vertex area.
The vibration damping system according to the invention may be constructed so that the electric machine comprises a rotor which rotates with the rotating constructional group and a stator which does not rotate with the rotating constructional group and which can be made to interact with the rotor so as to transmit counter-torque.
The electric machine may, for example, comprise a synchronous motor, an asynchronous motor or a reluctance motor.
The deflection mass arrangement may be arranged at least partially radially inside the electric machine and the deflection mass arrangement and electric machine may overlap in the axial direction at least in some areas. Of course, the deflection mass arrangement may also be arranged at least partially outside of the electric machine.
The stator of the electric machine may be arranged radially between a rotor of the electric machine and the deflection mass arrangement. Alternatively, the stator of the electric machine may be arranged radially outside of a rotor and the deflection mass arrangement. The dimensioning of the deflection paths and/or deflection masses may be carried out essentially independent from the construction of the electric machine when the electric machine and the deflection mass arrangement are arranged in axial succession.
As stated above, the electric machine is preferably controlled by the control device for partial elimination of movement irregularities, so that a remaining portion of the movement irregularities may be damped or eliminated by the deflection mass arrangement.
The present invention is further directed to a drive system comprising a drive unit and a vibration damping system according to the present invention.
When the drive unit is an internal combustion engine, the electric machine for generating counter-torque may also function as a starter arrangement for the internal combustion engine. Further, as was already mentioned, the electric machine may simultaneously function as a generator arrangement by which electric energy is provided for supplying electric energy consumers or for charging a battery.
For example, the deflection mass arrangement may be fixed in an area of the rotating constructional group fixedly connected with respect to rotation with the drive unit of the drive system. Alternatively, the deflection mass arrangement may be arranged in an area of a flywheel of a friction clutch of the drive system.
The present invention is further directed to a method for vibration damping in a drive system defined above, wherein the method comprises the following steps:
a) detecting information which indicates the occurrence of movement irregularities; and
b) controlling the electric machine for generating a counter-torque opposing the indicated movement irregularities.
In this method, the information indicating the occurrence of movement irregularities comprises at least one of the following quantities:
rotational speed of the drive unit;
temperature of the coolant of the drive unit;
position of at least one power output or actuating element of the drive unit;
output delivered by the drive unit; and
change in speed in the area of the rotating constructional group.
To counter occurring movement irregularities in a suitable manner, step b) may include generating a reference value for the counter-torque to be generated by the electric machine or a quantity in a relation to the counter-torque and adjusting an actual value of the counter-torque generated by the electric machine or the quantity related to the counter-torque to the reference value.
As was already mentioned above, the electric machine may be controlled to generate a counter-torque that essentially only reduces occurring movement irregularities so that the remaining part of the movement irregularities are damped or eliminated by the deflection mass arrangement.